1. Field of the Invention
The invention relates generally to method and apparatus for forming castings such as by lost wax processing and particularly to such methods and apparatus capable of use in forming dental castings of high quality.
2. Description of the Prior Art
The casting of useful items by processes known generally as "lost wax" processes has long been known. In such a process, a pattern is embedded in an investment material to form a mold from which the material forming the pattern can then be removed and replaced by a casting material such as a molten metal or metal alloy. The pattern itself is typically formed by an artisan skilled in the design and shaping of items such as jewelry, dental prostheses, etc. While patterns may be formed of various materials, it is usual that a pattern be formed of wax since wax can be readily removed from an investment material when a mold is formed in such a material such as by heating. The wax pattern embodies the shape and detail of an item which is to be produced in the mold which is eventually formed. The size, shape and detail embodied in the wax pattern must be duplicated by the investment material with which the pattern is surrounded to cause mold formation. The investment material itself is chosen for heat resistance and strength so that the wax pattern can be burned away in mold formation. The investment material must also be strong enough to allow a forceful introduction of a casting material such as a molten metal or metal alloy. Such processes have been commonly used in the formation of jewelry and similar items. However, a particular use for such processing involves the forming of dental crowns, bridges and similar dental prostheses. In the formation of devices of this nature, it is desirable that castings made from the molten metal be dense and not be subject to voids or conditions known as "shrink spot porosity" or the like. In order to form quality castings, particularly dental castings, present technology is improved by the sprue forming loop of the present invention which facilitates formation of a casting mold whereby a casting material can be quickly accelerated to the final destination within the mold since the casting material is not caused to negotiate right angles or sharp curves while traveling into the mold.